c# - 如何在我的类(class)中实现前置和后置自增/自减运算符？

Question

我想重载 ++ 运算符，以在我的 C# 类中使用运算符重载来使用前增量和后增量。但只有后增量才有效。如何使这两个功能在我的类(class)中起作用？假设我做了一个 ABC 类 -

using System;
using System.Collections.Generic;
using System.Text;

namespace Test
{
    class ABC
    {
      public int a,b;
      public ABC(int x, int y)
      {
        a = x;
        b = y;
      }
      public static ABC operator ++(ABC x)
      {
        x.a++;
        x.b++;
        return x;
      }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ABC a = new ABC(5, 6);
            ABC b, c;
            b = a++;
            Console.WriteLine("After post increment values are {0} and {1} and values of b are {2} and {3}", a.a, a.b, b.a, b.b);// expected output a.a = 6, a.b = 7, b.a = 5, b.b = 6 but not get that
            c = ++a;
            Console.WriteLine("After pre increment values are {0} and {1} and values of c are {2} and {3}", a.a, a.b, c.a, c.b); // expected output a.a = 7, a.b = 7, c.a = 7, c.b = 8 works fine
            Console.Read();
        }
    }
}

Answer 1

您的示例无法正确实现此一元运算符，如 17.9.1 一元运算符 中的 C# 规范中所指定:

Unlike in C++, this method need not, and, in fact, should not, modify the value of its operand directly.

这是您的示例，其中包含一些微单元测试:

using System;

class ABC
{
  public int a,b;
  public ABC(int x, int y)
  {
    a = x;
    b = y;
  }

  public static ABC operator ++(ABC x)
  {
    x.a++;
    x.b++;
    return x;
  }
}

class Program
{
    static void Main()
    {
        var a = new ABC(5, 6);
        if ((a.a != 5) || (a.b != 6)) Console.WriteLine(".ctor failed");

        var post = a++;
        if ((a.a != 6) || (a.b != 7)) Console.WriteLine("post incrementation failed");
        if ((post.a != 5) || (post.b != 6)) Console.WriteLine("post incrementation result failed");

        var pre = ++a;
        if ((a.a != 7) || (a.b != 8)) Console.WriteLine("pre incrementation failed");
        if ((pre.a != 7) || (pre.b != 8)) Console.WriteLine("pre incrementation result failed");

        Console.Read();
    }
}

您的代码失败是增量后的结果，这是由于您更改了作为参数传递的 ABC 实例而不是返回新实例。更正后的代码:

class ABC
{
  public int a,b;
  public ABC(int x, int y)
  {
    a = x;
    b = y;
  }

  public static ABC operator ++(ABC x)
  {
    return new ABC(x.a + 1, x.b + 1);
  }
}